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Tektronix DPScope II, User Manual

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Tektronix DPScope II User Manual Download Page 24

21 

 

2.6.1  CH1 / CH2 (Channel Offsets) 

Sets the channel offset for input channel 1 and 2, respectively. This lets you control where 
ground (zero Volts) is displayed on the vertical axis. First this expands the available voltage 
range for a given vertical resolution, e.g. at 1 V/div you could for example cover the range from 
0V to +20V, or alternatively from -20V to 0V. 
 
A second use for the offset is to move the two waveforms (CH1 and CH2) apart on the screen 
so they are easier to discern, even though in reality they cover similar voltage ranges (e.g. 0V to 
5V). 
 
The zero position for each channel is indicated on the left side of the waveform display with a 
colored marker (red for CH1, blue for CH2). If “Levels” is turned on in the display control frame, 
two dashed horizontal lines of same colors are drawn across the display as well at that vertical 
position (see picture below). 
 
To quickly move a slider 

back to center just press the button labeled “X”  (“center”) above the 

respective slider. 
 
Note: Due to the way the DPScope II is built you cannot change the waveform offset when the 
input is AC coupled. In this case the waveform center is fixed to the display center and the 
respective offset slider becomes inactive (greyed out). 
 

2.6.2  Trg (Trigger Level) 

This slider controls the trigger threshold. If the DPScope II is set up to trigger on one of the 
channels (CH1 or CH2), a trigger event occurs whenever the signal crosses this threshold with 
the desired polarity (rising or falling edge, respectively, or both rising and falling). 
 
The trigger level threshold for the chosen trigger channel is indicated on the left side of the 
waveform display with a green marker. 

If “Levels” is turned on in the display control frame, a 

green dashed horizontal line is drawn across the display as well at that vertical position. 
 
Usually the best approach with an unknown signal is to first display it with trigger in “Auto” 
mode. That way 

– although the waveform on the screen will not be stable – you can at least 

judge the voltage range that the signal spans, and set the trigger level marker somewhere within 
that range before setting the trigger source to the appropriate channel (see picture below). 
 
To quickly move the trigger slider back to center just press the button labeled “X”  (“center”) 
above the slider. 
 

Summary of Contents for DPScope II

Page 1: ...DPScope II User Manual Version 1 1 Feb 11 2017 ...

Page 2: ...le Shot 10 2 1 5 Averaging 10 2 1 6 Log to File 10 2 2 Display 11 2 2 1 CH1 CH2 11 2 2 2 REF1 REF2 11 2 2 3 Lines 11 2 2 4 Dots 11 2 2 5 Persist 12 2 2 6 Levels 12 2 2 7 Cursors CH1 CH2 12 2 2 8 X Y Mode 13 2 2 9 Frequency Spectrum FFT FFT Setup 14 2 3 Vertical 15 2 3 1 Voltage Scale 15 2 3 2 Probe Attenuation 15 2 3 3 Probe Coupling 16 2 4 Horizontal 16 2 4 1 Scope Mode Datalogger Roll Mode 17 2 ...

Page 3: ...7 4 Exit 23 2 8 Measure Menu 23 2 8 1 Measurements 23 2 8 2 Spectrum Analysis 25 2 8 3 DMM Display 26 2 9 Generator Menu 27 2 10 Calibration Menu 28 2 10 1 Probe Compensation 28 2 10 2 Level Compensation 30 2 11 Utilities Menu 31 2 11 1 Comm Setup 31 2 12 Help Menu 32 2 12 1 About 32 ...

Page 4: ...t the most from your DPScope II The XYZs of Oscilloscopes The ABCs of Probes You can download both documents either from the Tektronix website http www tektronix com or from the DPScope II website http www dpscope com Downloads If after reading through the documentation you still have questions regarding the DPScope II or want to provide feedback or suggestions for improvement do not hesitate to c...

Page 5: ... through a so called virtual COM port VCP meaning that while the physical connection is USB the interface driver makes the connection look like a legacy RS 232 COM port You can see such ports under COM and LPT ports in the Windows device manager To find out which virtual COM port the DPScope II uses go to Utilities Comm Setup in the DPScope II program the software will automatically detect which p...

Page 6: ...ayed Vertical Controls the input amplification attenuation for each of the two input channels Levels Sets the voltage offset for each channel and the trigger threshold level Horizontal Controls the sampling speed delay and sampling method Trigger Defines the trigger source On the bottom there is a status line that displays the cursor information right now the cursors are turned off which you use t...

Page 7: ...happen is that you no longer acquire a waveform and or see it on the screen If you get completely stuck simply close down the DPScope II program and start it again Move the offset sliders and see how the waveforms follow Now move the trigger level slider so the trigger level indicated by a green triangle on the left border of the waveform display is somewhere in the middle of the CH1 waveform the ...

Page 8: ...he trigger unless you can supply a suitable pre trigger signal to the second channel to trigger on If the waveform is periodic you may be able to use the Sweep Delay feature to trigger on one edge but look at the following one to get around this limitation 1 5 2 Pretrigger Mode In this mode the acquisition runs continuously until the trigger event e g the waveform crossing the trigger threshold fr...

Page 9: ...ery fast and efficient execution so the resulting frame rate number of full waveforms acquired and displayed is virtually as high as in Normal Mode the PC software does not even need to know that acquisition for fast equivalent sample rates is different from slower sample rate in either mode the scope simply reports when it has acquired a full waveform Thus as long as the input signal is repetitiv...

Page 10: ... the channel offset to the center of the screen That way your visible range spans from 10V to 10V assuming 1 1 probe attenuation which will capture most signals you encounter For larger signal use a 1 10 probe to widen the range even further don t forget to select the proper probe attenuation in the Vertical frame otherwise the displayed signal offset will be incorrect Whenever you use a new 1 10 ...

Page 11: ... this case each acquisition will hit the same point in the signal period just one period later each time so the displayed waveform on the screen will be a flat horizontal line rather than a sine wave clearly wrong If the signal frequency is a steady 1 1 kHz and the sample rate is 1 kHz each sample will be 1 10th of a period offset along the waveform and the resulting displayed waveform will be a v...

Page 12: ...acquires and displays only one record and then stops if No Avg no averaging is selected otherwise it will acquire the given number of records to average over and then stop This means that if you want to do a true single shot capture you need to set the averaging to No Avg In datalogger roll mode single shot and averaging is not available in this case the Run button simply starts the continuous acq...

Page 13: ...ing process used is not a simple arithmetic average over the given number of samples instead it uses exponential weighing i e earlier acquisitions have less weight than the more recent ones This is the digital equivalent to an analog R C low pass filter but unlike a filter in your signal path it will not degrade your signal bandwidth or rise time it will just filter out fast changes from one captu...

Page 14: ... CH1 looks at the chip select and CH2 looks at the clock signal and it triggers on the falling edge of the chip select signal Capture both signals with single shot mode and save CH2 to REF2 Now connect CH2 to the data line instead and repeat the capture You now have all three signals clock data chip select on the screen at the same time 2 2 3 Lines Checking this option will cause the scope to conn...

Page 15: ... off and Dots on 2 2 6 Levels Turns level markers and the trigger position marker in pretrigger mode on and off While the levels CH1 and CH2 offsets and the trigger threshold are also indicated with colored triangle markers on the left edge of the waveform display sometimes it is helpful to have rulers across the whole screen The trigger position in pretrigger mode tells you which portion of the w...

Page 16: ...between normal signal versus time or Y T waveform display and X Y display mode In X Y mode instead of plotting the CH1 and CH2 waveforms against time now CH1 determines the horizontal X position and CH2 the vertical Y position of each point A common application for this is to measure phase shifts e g in order to analyze reactive elements inductors capacitors It is usually easiest to first set up t...

Page 17: ...n most cases FFT mode works fine in auto trigger mode as long as the waveform is periodic and with sample rates low enough so several signal periods are displayed on the screen However make sure that your sample rate is at least 3 4 times your signal period otherwise aliasing will occur resulting in erroneous frequency domain pictures higher frequency components will get mirrored into the display ...

Page 18: ...fference to be correct you must of course actually have the probe set to the particular attenuation The scope has no way of knowing what you have the probe set to 2 3 2 Probe Attenuation The probe attenuation setting 1 1 and 1 10 respectively does not have any bearing on the actual input amplifier setup but rather tells the scope software how it must scale the measured data on the screen A 1 10 pr...

Page 19: ... that part that changes One example is the measurement of noise maybe just a few mV riding on a circuit s power supply voltage several Volts or some audio signal where components below 20 Hz are not audible anyway In these cases one wants to suppress the steady DC component so one can look at the AC component with high resolution a large DC component would otherwise force a rather coarse vertical ...

Page 20: ...puter The downside is that the record length is limited to these 800 points and for very slow sample rates the time between subsequent transfers becomes larger because it takes a while to capture 800 points at a slow rate Datalogger roll mode on the other hand is limited to relatively slow sample rates 1000 samples sec maximum which corresponds to 10 msec div but the length of the acquisition is u...

Page 21: ...to move left or right You can set the sweep delay to any value between 0 and 200 divisions be careful at slow timebase settings since during the sweep delay the DPScope II will be unresponsive In Pretrigger Mode such a sweep delay would not make much sense after all you choose this mode to look at the signal before or around the trigger instant so it is replaced by a trigger position selection thi...

Page 22: ...gger circuitry 2 5 2 Rising Falling Both The trigger polarity further specifies the required trigger condition Rising means the signal must cross the threshold from below and rise above the threshold i e a positive slope to cause a trigger Falling means the signal must cross the threshold from above i e a negative slope Both means the scope will trigger on a rising as well as a falling edge Of cou...

Page 23: ... the edge really was just a short noise spike as discussed above the trigger event will get suppressed and the DPScope II will keep waiting for a trigger This feature is especially valuable for slowly varying signals Note however that if your signal period becomes shorter than about one division activating the noise reject feature may prevent the DPScope II from triggering at all In this case eith...

Page 24: ...ange the waveform offset when the input is AC coupled In this case the waveform center is fixed to the display center and the respective offset slider becomes inactive greyed out 2 6 2 Trg Trigger Level This slider controls the trigger threshold If the DPScope II is set up to trigger on one of the channels CH1 or CH2 a trigger event occurs whenever the signal crosses this threshold with the desire...

Page 25: ...l settings like acquisition mode vertical scales time scale trigger setup etc to a file 2 7 3 Export Data Exports the currently displayed waveforms to a text file The file contains both scope waveforms CH1 and CH2 as well as both reference waveforms REF1 and REF2 File format is standard CSV comma separated values format which you can open and process in Microsoft Excel or any standard text editor ...

Page 26: ...ake the measurements and also which measurements to take The values get updated after every acquisition If you have already acquired the signal and only afterwards bring up the Measurements panel simply press Update Values to perform the calculation based on the currently displayed waveforms Do not change vertical or horizontal settings like gain or offset between the acquisition and the calculati...

Page 27: ...near interpolation to improve resolution and accuracy of the results This way the resolution of the measurements is much finer than one sample period Averaging can significantly improve the accuracy especially for the level measurements Measurements slow down the acquisition process somewhat Turn them off close the measurement panel for maximum screen update rate ...

Page 28: ...gh 100 Period time between subsequent rising edges crossings of the 50 point midlevel or falling edges if there aren t two rising edges on the screen Frequency 1 period Duty cycle time spent above 50 during one period relative to the length of the period duty_cycle pos width period Pos width time spent above 50 during one period Neg width time spent below 50 during one period The threshold drop do...

Page 29: ...efault of 7 means it uses 3 points each to the left and to the right of the peak s maximum This method ensures a very precise determination of the actual frequencies A setting of 1 is possible but may lead to erroneous results so a minimum of 3 is recommended On the other hand choosing to large a width will include a considerable amount of non harmonic noise in each calculated peak again affecting...

Page 30: ...keep in mind the DPScope like any other oscilloscope is an instrument mainly geared towards display of signal changes over time not as a voltmeter Thus the voltage accuracy or resolution cannot compete with a dedicated DMM it is limited by the accuracy of the input divider resistor the internal voltage reference and several other factors so it should only be used as a rough guidance or to observe ...

Page 31: ...ycle To perform probe compensation attach the probe s signal pin to the CAL output and the probe s ground lead to the GND output on the back of the scope The display will show roughly two periods of the calibration signal 3 3V amplitude square wave Depending on the probe you use 1 1 or 1 10 you may need to adjust the vertical scale and offset to get a decently sized signal on the screen Refer to t...

Page 32: ...29 ...

Page 33: ...ight out of the box without you needing to perform this procedure It can however be a good idea to execute compensation when using a new set of 1 10 probes because it will optimize offset and gain settings for each particular probe To perform this compensation you will need a set of two switchable 1 1 1 10 probes Normally the process is fully automated apart from you attaching the probes and conne...

Page 34: ... in the appropriate boxes the scope will write the new values to the scope If there are problems with the results the software highlights red background the values that are outside the tolerance and you will get prompted as to whether you want to overwrite the currently stored values nevertheless 2 11 Utilities Menu 2 11 1 Comm Setup Displays the virtual COM port the DPScope II is connected to Sin...

Page 35: ...ersion and build date of your software the version of the scope s firmware and finally the serial number of your scope please always include this information when submitting bug reports or support requests The panel also shows the support contact info ...

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